<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title> 
</head>
<body>
<script type="text/javascript">

//var a = (1,2,3,4,5)
//alert(a);
//var a = 1,2;
//alert(a);
//alert('1','3','4')
//alert(1,2,3,4);//1,2,3,4   o 1
//alert((1,2,3,4));//不弹     o 4


</script>
</body>
</html>